Various kinds of methods for pairing between communication devices have been proposed. Examples of the methods include a method using a personal identification number (PIN), push-button methods (see Patent Literatures 1 and 2), and a near field wireless communication method (see Patent Literature 3). Each communication device shares a secret key with a target by pairing with the target. Each communication device may be configured to be capable of pairing according to a plurality of kinds of pairing methods.